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Date: Mon, 2 Aug 2010 00:15:51 +0900
From: Minchan Kim <minchan.kim@gmail.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>, Andrew Morton <akpm@linux-foundation.org>,
        Dave Chinner <david@fromorbit.com>, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@infradead.org>,
        Chris Mason <chris.mason@oracle.com>,
        Jens Axboe <jens.axboe@oracle.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH 4/6] writeback: sync expired inodes first in background
 writeback
Message-ID: <20100801151551.GA8158@barrios-desktop>
References: <20100722050928.653312535@intel.com>
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Hi Wu, 

> Subject: writeback: sync expired inodes first in background writeback
> From: Wu Fengguang <fengguang.wu@intel.com>
> Date: Wed Jul 21 20:11:53 CST 2010
> 
> A background flush work may run for ever. So it's reasonable for it to
> mimic the kupdate behavior of syncing old/expired inodes first.
> 
> The policy is
> - enqueue all newly expired inodes at each queue_io() time
> - enqueue all dirty inodes if there are no more expired inodes to sync
> 
> This will help reduce the number of dirty pages encountered by page
> reclaim, eg. the pageout() calls. Normally older inodes contain older
> dirty pages, which are more close to the end of the LRU lists. So
> syncing older inodes first helps reducing the dirty pages reached by
> the page reclaim code.
> 
> CC: Jan Kara <jack@suse.cz>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
>  fs/fs-writeback.c |   23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
> 
> --- linux-next.orig/fs/fs-writeback.c	2010-07-26 20:19:01.000000000 +0800
> +++ linux-next/fs/fs-writeback.c	2010-07-26 21:10:42.000000000 +0800
> @@ -217,14 +217,14 @@ static void move_expired_inodes(struct l
>  				struct writeback_control *wbc)
>  {
>  	unsigned long expire_interval = 0;
> -	unsigned long older_than_this;
> +	unsigned long older_than_this = 0; /* reset to kill gcc warning */

Maybe I am rather late. 

Nitpick. 
uninitialized_var is consistent. :)

I haven't followed up this patch series. but his patch series is a fundamental way 
to go for reducing pageout. 
-- 
Kind regards,
Minchan Kim